1. Technical Field
The present invention relates to a multi-layer fabric for paper-making and in particular, to a multi-layer fabric for use in a wire part of a paper-making process in which paper-fiber dispensed water is passed onto said fabric and dewatered to form a paper web having a smooth surface.
2. Background Art
Early paper making fabrics were of metal wires made from phosphor bronze material. Recent ones are made of plastic wire consisting essentially of synthetic resins. Further, the plastic wires, which were originally of a single layer structure, have been replaced by rigid double layer structure wires in order to improve the quality of the paper sheet formed on the plastic wires and to speed up the paper making process. As this type of fabric there are known a single warp-double weft layer type fabric, i.e. a fabric consisting of a a double layer of weft threads interwoven with a single layer of warp threads, and a double warp-double weft layer type fabric, i.e. a fabric consisting of a double layer of weft threads combined with a double layer of warp threads. These double layer fabrics have advantages in that, on one hand, a paper-side surface of the fabric can provide a smooth paper surface because the paper-side of the fabric can have a finer weave pattern, and on the other hand, a machine-side surface of the fabric can be constituted by larger size rigid materials so that the machine-side surface can withstand abrasive wear by supporting members when the fabric is rotated at high speed.
In a single warp-double weft layer type fabric, a single warp appears on both sides, i.e. the paper-side and the the machine side. In contrast, however, in a double warp-double weft layer type fabric, an upper layer and a lower layer each have a combination of respective warps and wefts. Therefore, this fabric provides the above advantages more effectively.
However, actually, the double warp-double weft type fabric has disadvantages resulting from binding the upper-most layer and the lower-most layer. This type of multi-layer fabric is known, for example, from the Japanese Patent Publication No. 59-42116 corresponding to U.S. Pat. No. 3,885,603. The binding manner shown in this publication results in unevenness or ruggedness on the paper-side surface of the fabric to thereby produce wire-marks on the paper sheet formed on the fabric.
FIG. 6 shows a schematic sectional view taken along a binder thread 10 of the fabric consisting of a double layer of weft threads combined with a double layer of warp threads in which the upper-most layer A and the lower-most layer B are integrally bound by a method similar to the one disclosed in said publication.
Referring to FIG. 6, said disadvantages will be explained in more detail.
In FIG. 6, reference numeral 6 denotes a warp of the upper-most layer A, reference numeral 7 denotes a weft of the upper-most layer A, reference numeral 8 denotes a warp of the lower-most layer B, and reference numeral 9 denotes a weft of the lower-most layer B.
The fabric illustrated in FIG. 6 consists of the upper-most layer A having a plain textile weave 1/1 and the lower-most layer B having a twill textile weave 2/1 which is coarser than the upper-most layer A, the layers A and B being integrally bound by means of the binder thread 10 having a diameter smaller than the warp and weft threads. This textile weave of the fabric is typical of ones now actually utilized in paper-making machines.
Generally, the plain textile weave 1/1 of the upper-most layer A has more upper-knuckles of warps and wefts than other textile weaves. These knuckles support a paper-web formed thereon and are evenly arranged at the same level. This makes it possible to obtain a paper surface which is smoother and has less wire-marking.
However, when the upper-most layer A and the lower-most layer B are bound as shown in FIG. 6, the warp 6a intersecting with the binder thread 10 is pulled downwards, so that on both sides the warps and wefts adjacent the intersecting point, i.e. the binding point, are also downwardly displaced, resulting in dimples 11 as shown by hatching in FIG. 6. The paper web formed on the upper surface of this fabric is thicker at the portion corresponding to the dimples 11 than other portions, resulting in varying thickness of the paper sheet. Further, since these thicker portions are formed on respective binding points or binding portions, these thicker portions appear as diagonal or lateral streak patterns on the paper. Such unevenness of the paper sheet surface results in impaired printability of the paper sheet.
Further, since the binder thread 10 is interwoven with the warps 6a in such a manner that it is wedged in between wefts 7, the distance between wefts 7 at the binding portions is expanded, and the adjacent warps 6 also are pushed through the wefts 7 so that the distance between the warps 6 are also expanded. As a result, it is impossible for the fabric to maintain the uniform wire mesh size thereof.
Further, since the binder thread 10 is wedged between warps 6a and 6 and between wefts 7 and 7, the wire mesh space is greatly decreased.
This results in uneven thickness of the paper web because of partially uneven dewatering from the paper web, and this uneven thickness appears as longitudinal, lateral, or diagonal wire-marks on the paper sheet, leading to significantly impaired paper quality.
As described above and shown in FIG. 6 and said Japanese Patent Publication No. 59-42116, even when the binder thread 10 has a smaller diameter than those of the weft and warp, the prior art fabrics have the above disadvantages, and when the upper-most layer and the lower-most layer are bound by means of the warps or wefts of the fabric without using the binder thread 10, the above disadvantages will become more notable, and as a result, these fabrics cannot be practically utilized.
In the present specification and claims, "warp" and "weft" mean two groups of threads interwoven with each other and intersected at a right angle (as seen in the plan view) with each other, one group being called the "warp" and the other group being called as the "wefts". Accordingly, the "warp" and "weft" are independent from whether they extend longitudinally or laterally during weaving, or whether they extend in a machine direction or in a cross-machine direction during use. Thus they are interchangeable as textile weave.